I am leaning more toward the gearing too, but look into capacitor mod too. The MM is not designed for hard running on 4s. I know how you feel w/ drilling holes in $135 electronics, I did mine w/ my eyes closed and teeth clenched. but it will be ok.
Don't worry about dirt, if your savey enough to take it apart to drill holes you can take it apart to clean it...ever see the inside of a PC? I'd worry more about water!! Holes or not don't make much of a diff then anyway. Search some of the forums for Cap mods... GriffinRU on this forum does a great one.
here is his
http://forum.rcdesign.ru/index.php?a...showentry=4093
...or try these
http://www.rcuniverse.com/market/item.cfm?itemId=392947
http://www.rc-monster.com/forum/show...mamba+max+mods
click and paste to address bar if links don't work.